Fixed element rotor structures

ABSTRACT

The invention relates to inertial energy storage devices wherein a central hub holds a multiplicity of anisotropic filaments, the filaments extending from the hub in fixed relation thereto and in parallel planes perpendicular to an axis of rotation through said hub. Each filament extending from the central hub is so disposed within the structure that the stress component imposed on said filament acts uniaxially along its length.

United States Patent Rabenhorst [54] FIXED ELEMENT ROTOR STRUCTURES [72]Inventor: David W. Rabenhorst, Silver Spring,

[73] Assignee: The Johns Hopkins University, Baltimore, Md.

221 Filed: July 30,1971 2'1 Appl. No.: 167,643

521 U.S.Cl... ..74/572, 74/5 511 Int.Cl ..Fl6h33/02 [58] Field of Search..74/572,5; 15/l79, 181

[56] References Cited UNITED STATES PATENTS 1,514,530 2/1926 Adams"ls/181 [451 Oct. 17, 1972 Peterson 15/1 79 Primary Examiner-William F.*ODea Assistant Examiner-J. D. Shoemaker Attorney-John S. Lacey ABSTRACTThe invention relates to inertial energy storage devices wherein acentral hub holds a multiplicity of anisotropic filaments, the filamentsextending from the hub in fixed relation thereto and in parallel planesperpendicular to an axis of rotation through said hub. Each filamentextending from the central hub is so disposed within the structure thatthe stress component imposed on said filament acts uniaxially along itslength.

21 Claims, 13 Drawing Figures Charvat ..15/179 PAIENTEDum 1 1 m2 v 3.698. 262

sum 1 or 6 INVENTOR. DAVID w. RABENHORST F I 6. 3a

PATENTED CH m2 3.698262 SHEET 2 0F 6 INVENTO DAVID w. RABENHORPATENT'EYDBET H 1912 3.698, 262

SHEET 3 [IF 6 INVENTOR. DAVID W. RAB ENHORST V PATENTEUH 11 1972 SHEET t[If 6 INVENTOR. F I 8 7 DAVID w. RABENHORST PATENTEDMHHQH 3.s9e,-2s2

' I SHEEI 5 OF 6 INVENTOR. DAVID W. RABENHORST FIXED ELEMENT ROTORSTRUCTURES STATEMENT OF GOVERNMENT INTEREST The invention hereindescribed was made in the course of or under a contract or subcontractthereunder, with the Department of the Navy.

CROSS-REFERENCE TO RELATED APPLICATION The present invention comprises anovel modification of the invention described in co-pendingUS. Pat.application, Ser. No. 60,047, filed July 31, 1970, entitled FilamentRotor Structures, by the same inventor.

BACKGROUND OF THE INVENTION A. Field of the Invention v The inventionrelates to energy storage devices, such as flywheels, and particularlyto performance-optimized high-speed rotary structures. Application ofthe invention ranges from use as the sole power source of a quiet,pollution-free urban vehicle to use as a home emergency power supplyunit.

. B. Description of the Prior Art The flywheel has been used forcenturies as an efficient energy storage device. Since the flywheel isan inertial device governed by the laws of kinetic energy, maximumperformance is attained at maximum speed, the performance beinggenerally quadrupled with a two-fold increase in speed. The speed of therotating body, however, cannot be increased beyond its burstingof anisotropic steel structure is substantially less than that obtainablewith modern anisotropic filamentary materials. High strength filamentstypically exhibit substantially greater strength-to-densitycharacteristics over the best isotropic materials, such as steel ortitanium. Only a small portion of this strength advantage can be used inthe prior art flywheels due to the inherent isotropic stresses in thesestructures. In the rim type flywheel, stresses normal to the woundfilaments exist at all locations other than the outer edge.Additionally, the problem of attachment of the rim to the hub, requiringadditional weight, has been a principal factor inhibiting furtherdevelopment of this flywheel structure.

I The present inertial energy storage device offers substantialimprovement in useable energy density due not only to the advantageousutilization of the high uniaxial strength of filamentary materials, butalso to the more efficient packaging density provided by the invention.The structure Y of the invention permits maximum utilization of theuniaxial strength of each filament while packaging a multiplicity offilaments within an extremely compact volume.

The significance of the present energy storage device is best understoodby its application to the urban vehicle. Although flywheels have beenused in short-range vehicles, such as in the Swiss Oerlikon bus and inthe British Gyreacta transmission, those devices produced only aboutthree watt-hours per pound. Thus, energy density of the devices was evenlower than that of available lead-acid batteries at the same dischargerate. However, certain characteristics of flywheels caused their use inpreference tostorage batteries, despite the problems then encountered inthe use of flywheel structures. Firstly, the flywheel can be charged anddischarged virtually an infinite number of times without degradingperformance. Secondly, it can becharged at any reasonable rate. Thirdly,it can be discharged at any rate within the design limitations ofancillary equipment without degrading performance. These capabilitiesare largely responsible for the proposed use of flywheels inpollution-free urban vehicles. In most previous proposals, the rapiddischarge capabilityof the flywheel has been primarily used to lendincreased acceleration power to the vehicle in order to minimize theoverall size of the main propulsion power plant. The present energystorage device provides a power plant of sufficient energy density toalso enable its economic and practical use as the primary energy sourcein an urban vehicle.

SUMMARY OF THE INVENTION In a first embodiment, the invention provides ahigh performance inertial energy storage device wherein a central hubholds a multiplicity of uniaxial filamentary elements in radiatingdisposition to the hub. In particular, straight anisotropic rods orcomposite rods of filamentary or whisker materials are disposed aroundthe periphery of the central hub in substantially parallel relationtothe major stress component acting on the rods during rotation thereof.As is the case with other flywheel devices, the performance ofthepresent in vention is directly proportional to the specific strength ofthe material used in its construction. By utilizing the large specificstrengths of filamentary materials, i.e., by

aligning the individual filaments substantially parallel to the majorstress component which acts along the axis of each individual filament,a dramatic energy density increase in the total structure results, thusmaking a flywheel-type structure useful to a wide variety ofapplications beyond the capabilities of prior art rotary energy storagedevices. Since the invention allows the filaments in the device to be inline with the respective force vectors generated by their own rotatingmasses, virtually all of the available strength of the filamentarymaterials is effectively used, thereby maximizing packaging density(watt-hrs/pound and watt-hrs lunit vol.) without performancedegradation.

In a second embodiment of the invention, a central hub having arcuateinternal support surfaces holds a multiplicity of anisotropic elementsin fixed, pre-determined positions within the energy storage device,the- Accordingly, it is an object of the invention to provide a highpower-density energy storage device which also has a high energy densitycapability.

It is a particular object of the invention to provide a rotary energystorage member comprised of anisotropic filaments or rods radiating froma central hub, each said filament being substantially parallel to themajor local stress component acting thereon.

A further object of the invention is to provide a rotary energy storagemember comprised of anisotropic filaments or rods held in fixedpositions within a central hub, the filaments each being fanned out to apredetermined curvature.

Another object of the invention is to provide an energy storage devicewhich can be readily and efficiently made from a large number of smalldiscrete rod-like elements in order to minimize the likelihood ofsimultaneous failure of all such elements and thus maximize the safetyof the device.

It is also an important object of the invention to provide a rotorstructure having inherent gimballing capability about a stationary spinaxis in order to minimize gyroscopic loads on the rotor and its spinbearings.

A still further object of the invention is tor provide a denselypackaged", efficient, economical, high performance and pollution-freeenergy storage device useful in an urban vehicle for alleviating theincreasing contribution of motorized vehicles to noise and air pollutionproblems.

Additional objects, advantages, and uses of the invention will becomeapparent from the following detailed description of the preferredembodiments thereof.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an enlarged perspective viewof a single, essentially uniaxial filament illustrating the major stresscomponent acting on the filament during rotation thereof;

FIG. 2 is a plan view of a circular brush rotor fabricated according tothe invention, the rotor being shown partly broken away to illustratefilaments aligned along local stress vectors;

FIG. 3a is a section of the circular brush rotor of FIG. 2 taken alongline 3-3 thereof;

FIG. 3b is an enlarged detail elevation of a portion of the rotor ofFIG. 30;

FIG. 4 is an idealized detail plan view of a greatly enlarged portion ofthe peripheral surface area of the hub;

FIG. 5 is a perspective of a modified rotor in which the hub and rodsare laminated together in alternating fashion to build up a rotorstructure;

FIG. 6 is a plan view of another modification of the invention, therotor employed being fitted with a gimballing device to provideattachment to a rotatable shaft;

FIG. 7 is a section of the rotor of FIG. 6 taken along line 77 thereof;

FIG. 8 is a perspective of still another embodiment of theinvention-illustrating a rotor having diverging, or fanned out elements;

FIG. 9 is an enlarged detail plan view of aportion of v the hub and ofthe elements comprising the rotor of FIG. 8;

' have most often been used in the construction of FIG. 10 is aschematic illustrating the relationships for determining the position ofeach element within the rotor; and

FIGS. 11a and 11b are charts showing graphically the relationships shownin FIG. 10.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The performance, i.e., thestored kinetic energy of a rotating body, is directly proportional totheuseable specific strength of the material used in the fabrication ofthe body. Isotropic materials, such as solid steel,

kinetic energy structures, or flywheels. However, the best isotropicmaterial exhibits only a small fraction of the strength-to-density ofanisotropic materials, such as music wire, Fiberglas or boron filaments,for example. It will thus be understood that a flywheel rotor configuredto maximize the anisotropic strength characteristics of uniaxialfilamentary or whisker materials is capable of increased performancerelative to flywheels composed of isotropic materials. In a firstembodiment, the present invention not only provides a rotary structurecomprised of straight anisotropic filamentary material which maximizesperformance and also permits considerably increased rotor weight withina given volume, hence more energy per volume, relative to prior straightfilament rotor structures. This increase is primarily due to theinclusion within the present rotor structure of a circular hub andanisotropic elements around the full periphery of said hub. Additionaladvantage is provided by the ability of the present structure to allowalignment of each radial element in the structure along the local stressvector acting on said element.

For illustration of the concept embodied in the invention, a singlefilament or thin rod 10 is shown in FIG. 1 to be spinning about an axisnormal to its longitudinal axis. If the diameter of the filament 10 isinfinitely small, the total stresses in it are directed along its lengthfrom its spinning axis towardits ends, i.e., the direction of thecentrifugal forces acting on it, said centrifugal forces, for thesituation described, being the only forces acting on it during rotation.If the filament 10 were the only element in a flywheel or rotatingstructure, all of its allowable strength at its center would contributeto the kinetic energy of such a flywheel. However, in order to obtain arotary structure of sufficient mass to possess utility, a plurality offilaments have previously been bound together in mutually parallel ornear parallel relation by suitable hub means. While producingsubstantially improved energy storage structures, such filament rotarystructures are subject to minor loads which are not directed along thelongitudinal axes of the filaments, such loads tending to reduce theenergy storage capability of the structures. In the embodiments of thepresent invention, the filaments are disposed within the rotarystructure so that the local stress vector acting on each filament iseffectively directed along its longitudinal axis.

A circular brush rotor is seen at 5 in FIGS. 2 and 3a to comprise aplurality of filaments 10 radially extending from a central cylindricalhub 12. The hub 12 has two centrally mounted shaft members 14 extendingfrom either end thereof, the longitudinal axis extending through'theshaft members 14 being coincident with the axis of rotation 6 of therotor 5. The hub 12 may be formed of any essentially isotropic materialhaving high specific strength or may be formed from layers offilament-wound composite materials 1 joined into a laminate in a mannerto be described further hereinafter. The filaments 10 are chosen from avariety of anisotropic materials having essentially uniaxial loadbearing capabilities, e.g., Fiberglas, graphite, quartz, or boronfilamentary rods.

The filaments 10 extend radially from the cylindrical surface 16 of thehub 12 around the full periphery of said hub. As can be seen morereadily in FIG. 3b, each filament 10 has its inner end portion securedin a hole 18 in the surface 16 of the hub 12. The inner ends of thefilaments l are preferably secured in the holes 18 by a suitableadhesive,'such as epoxyJSince the inner ends of the filaments 10 extendinto the holes 18 for a finite distance-and adhere to the walls of saidholes over the full areas of mutual contact, a bond of sufficientstrength to prevent pull-out of the filaments during high-speed rotationof the rotor 5 is planes The filaments areseen in FIG. 3a to extendradially from the hub 12 in successive planes perpendicular to the axisof rotation 6 of the rotor 5, co-planar filaments 10 extending inwardlytoward a co-planar point lying on said axis of rotation.- Essentially,if each filament 10 were extended inwardly to the center of .the rotor5, the filaments would meet at points along the axis of rotation 6.Thus, if a plane is taken through the rotor 5 perpendicular to the axisof rotation 6, each filament 10 lying in that plane is coincident with aradius extending from the geometrical center of the plane, saidgeometrical center lyingon the axis of rotation 6 of the rotor 5.

The holes 18 in which the inner ends of the filaments 10 are held may beformed by chemical milling, stamping, or in someother suitable manner.However, a particular manner of accomplishing attachment of the elementsto the hub is indicated in FIG. 4. In this view, the hub 12 iscomposedof successive disc-like layers 20. Semi-cylindrical depressions22 are pressed into upper 6 laminated disc hub 12 composed of highstrength steel.

In the modification of FIG. 5, a high strength, lightweight hub 21 isformed by alternately bonding together layers of the filaments l0 andfilament-wound sheets 23. The layers of filaments l0 and sheets 23 arelaminated together with an epoxy adhesive 25 to give solid bi-axiallaminar strength properties to the hub 21. The hub 21 therefore hasgreater strength-to-density and less weight than a hub fabricated fromisotropic material. g The rotor of the present invention may begimballed, as shown in FIGS. 6 and 7, to minimize gyroscopic precessionloading on the rotor and on bearings used to support shafting holdingthe rotor. The internal gimbal device shown generally at 30 avoids thenecessity-for otherwise having large external gimbal rings andassociated bearings. More importantly, rotor shaft 32 does not have tobe gimballed, enabling its outputto be used directly. The gimbal device30 is seen to comprise a cruciform member 34 having shaft pins 36extending therefrom along the minor axis of the member and gimbal pins38 extending along the major axis of said member. The cruciform member34 is disposed within a transverse opening 40 in the shaft 32, the shaftpins 36 having their outer ends rotatably received within alignedbearings. r

A circular brush rotor 44 is fitted with a hub 46 having an axialchannel 48 disposed therein for receiving the shaft 32. The ends of thegimbal pins 38, which extend longitudinally from the transverse opening40, are rotatably received within aligned bearings 50 disposed in thewall which defines the channel 48. The rotor 44 is thus fully gimballedin the axial channel 48. For any foreseeable vehicular application inwhich the rotor 44 and lower faces 24 and 26 of the layers 20, exceptthe top and bottom surfaces of the uppermost and lowermost layers,respectively, so that the depressions 22 of one layer 20 confront thoseof adjacent layers, the longitudinal axes of said depressions 22extending radially from the geometrical centers of the faces 24 and 26.The inner ends of the filaments 10 are then placed into confrontingsemi-cylindrical depressions 22 of adjacent layers 20. The diameter ofthe filaments 10 may typically be 0.03 inch, the layers 20 having athickness of 0.04 inch to provide maximum packaging with reasonableseparation between successive layers of filaments. The lateraldisplacement from center-line to centerline of the filaments 10 may alsoreasonably be 0.04 inch. The disc-like layers 20 may be vacuum weldedalong adjoining .upper and lower faces 24 and 26 to assure high strengthfor the hub 12. I

The actual number of the filaments 10 per unit area of the cylindricalsurface 16 is determined by the capacity of the hub 12 to withstand thecombined loading on said filaments within said unit area and the loadingdue to the rotation of the hub itself. Typically, uniaxial Fiberglasrods of the dimensions noted above, i.e., 0.03 inch diameter, proveuseful with the is to be used with a stationary vertical spin axis,reasonable gimbal limits, allowing tiltingof the hub, are provided bythe internal gimbal device 30.

FIGS. 8 and 9 illustrate still another embodiment of the invention,i.e., a rotor, shown generally at 60, which has elements contoured intoa fixed-fanned brush shape. The rotor 60 comprises a unitary central hub62 having arcuate side walls 64 curved toward each other and spaced byflat, parallel upper and lower walls 66 and 68, the walls 66 and68terminating in arcuate edges 69. Shaft members 70 are attached to thewalls 66 and 68 and extend above and below said walls on the axis ofrotation of the hub 62. An assembly of anisotropic filament-likeelements 72 extends through a central longitudinal cavity 74 in the hub62, the elements 72 being held in fixed, predetermined positions withinsaid hub. As can be seen more clearly in FIG. 9, the elements 72, exceptelements 72a at the exact midpoint of the assembly which are straight,are held in fixed, precontoured, arcuate positions within the hub 62 bya matrix material 76, such as epoxy. The shape of each element 72 isdetermined by means to be described hereinafter. I

Although FIG. 9 shows for simplicity only a portion of one co-planarlayer of elements 72 in the rotor 60, the actual structure of the rotormay be appreciated by reference to axes of symmetry 78 and 80. Thelongitudinal axis of symmetry 78 is coincident with the longitudinalaxis of the rotor 60, the pattern of the elements 72 shown to the rightof the axis 78 in FIG. 9

being duplicated in mirror image to the left of said axis 78. Similarly,the pattern of the elements 72 above the transverse axis of symmetry 80in FIG. 9 is duplicated in mirror image below the axis 80. Thelongitudinal and transverse axes of symmetry 78 and 80 intersect at thegeometrical midpoint of the axis of rotation of the rotor 60. Thestructure of the rotor 60 is completed by building up in stackedrelation a plurality of layers of the pattern of elements 72 thusdescribed.

The elements 72 and 72a may be of the same length or, alternately, oneor more of the elements 72a may be made longer than the remainingelements 72 as a safety measure. The additional loading on an extra longelement 72a would cause that element to fail first if the speed of therotor 60 exceeded design limitations. By being disposed centrally in thestructure, failure of the element 72a would not produce substantialimbalance while providing a warning of excessive speed or imminent rotorfailure.

Straight elements 72a, contained in a plane perpendicular to the upperand lower walls 66 and 68 and extending through the longitudinal axis ofsymmetry 78, remain straight during rotation of the rotor 60, therebyfully utilizing the inherent strength-to-density of said elements 72a tocarry the tension loading, or stress, which is directed along the lengthof said elements. The elements 72 on either side of the straightelements 72a thus described are held in contiguous relation along thetransverse axis of symmetry 80, each element 72 diverging from the axis80 in progressively greater degrees of curvature, i.e., the innerelements 72 having a greater radius of curvature than the outer elements72, the element 72b adjacent to the straight element 72a having thelargest radius of curvature and the outermost element 72c having thesmallest radius of curvature. The inner surfaces 82 of the side walls 64of the hub 62 are formed with a radius of curvature equal to that of theoutermost elements 720. Thus, midportions of the elements 72c arecontiguous to and are supported by the surface 82 of the wall 64 alongthe full length of said wall. The remaining elements 72 are held inplace and supported by the matrix material 76 which surrounds themidportions of said elements within the central cavity 74.

As can be seen with reference to FIGS. 9 nd 10, those portions of theelements 72 which extend externally of the hub 62 are aligned alongextended radii of an imaginary circle 83 defined in part by the arcuateedges 69 of the hub 62. The elements 72 must be positioned within thehub 62 with the proper curvature in order for the portions of theelements 72 external of the hub to be directed as described. Althoughthe straight elements 721: are the only elements within the rotor 60which are positioned to permit maximum utilization of thestrength-to-density of the elements, proper choice of the radii ofcurvature of the remaining elements 72 hub 62 may be determined from therelationships illustrated in FIG. 10. In FIG. 10, a single element 72 isschematically shown. in its predetermined location within the rotor 60,the displacement of the element 72 from the axis of rotation being takenas normal from the longitudinal axis of said element to the longitudinalaxis of symmetry 78. That portion of the element 72 extending beyond thecircle 83, which circle is defined in part by the arcuate edges 69 ofthe hub 62,1ies along an extended radius r of the circle 83 drawn to thepoint of intersection of the longitudinal axis of the element and saidcircle. The tangent to the circle 83 through the aforementioned point ofintersection defines the radius of curvature R of that portion of theelement 72 lying within the hub 62. In particular, theradius ofcurvature R is that portion of the tangent lying between theaforementioned point of intersection on the circle 83 and theintersection of the tangent with the extended transverse axis ofsymmetry 80. The angle 0 between the radius of curvature R and theextended transverse axis of symmetry is identical to the angle definedby the longitudinal axis of symmetry 78 and the extended radius r withwhich the element 72 aligns beyond the circle 83.

The relationships between the above described values define the positionof the element 72, which relationships are shown graphically in FIGS.11a and 11b. FIG. 11a shows the relation between the angle 0 and D/r,while FIG. 11b illustrates the relation between R/r and D/r. For a givendisplacement D and radius r, the radius of curvature R of each element72 may be determined from either FIG. Ila or 11b. Alternatively, giventhe displacement D and the radius r, the radius of curvature R for thegiven element 72 may be directly determined from the relationship:

1 r f 2 D In practice, the stress loss encountered due to bending of theelements 72 should be limited to 20 percent or less to maintainperformance capabilities of the rotor 60. The following relationshipallows determination of the maximum desirable radius of curvature R fora given element 72:

S t Y/ 4R 2 where: Q I

S Bending stress loss;

t= thickness of an element;

Y= modulus of elasticity of the material;

R radius of curvature.

The rotor 60 may be gimballed according to the principles described inthe previously mentioned co-pending patent application Ser. No. 60,047,by the present inventor.

It is to be understood that the foregoing description of the inventionis illustrative, and that various modifications to the structure andmanner of fabrication of the rotors disclosed herein may be made withoutdeparting from the scope of the invention.

Iclaim:

1. An energy storage device having an axis of rotation extendingtransversely therethrough, comprising a plurality of anisotropic,filament-like members having maximum strength-to-density along theirlongitudinal axes, the longitudinal axes of portions of said membersextending radially from the axis of rotation of the device,

hub means for holding the members in planes perpendicular to the axis ofrotation of the device, the axis of rotation of the device beingcoincident with the longitudinal axis of said hub means, I the hub meansbeing comprised of disc-like layers of material, adjacent layers havingconfronting semicylindrical depressions in the upper and lower facesthereof, the confronting semi-cylindrical depressions cooperating toreceive portions of each of the members within the hub means and saidlayers clamping said portions of said members i in said depressions. 2.The energy storage device of claim 1 wherein the adjacent layers arejoined along respective upper and lower faces.

3. An energy storage device having an axis of rotation extendingtransversely therethrough, comprising a plurality of anisotropic,filament-like members having maximum strength-to-density along their longitudinal axes, hub means for holding the members in planesperpendicular to the axis of rotation of the device, the

axis of rotation of the device being coincident with thelongitudinalaxis of said hub means and the longitudinal axes of the members beingaligned along radii emanating from points along the axis of rotation,the members being disposed around the 7 full periphery of the hub means,

the hub means being comprised of disc-like layers of material, adjacentlayers having confronting semicylindrical depressions in the upper andlower faces thereof, the confronting semi-cylindrical depressionscooperating to receive portions of each of the members within the hubmeans and said layers clamping said portions of said members in saiddepressions. i

4. An energy storage device having an axis of rotation extendingtransversely therethrough, comprising a plurality of anisotropic,filament-like members having maximum strength-to-density along theirlongitudinal axes, the longitudinal axes of portions of said membersextending radially from the axis of rotation of the device, and

hub means comprising layers of parallel planar spiral wound filamentsdisposed in alternation with respect to parallel layers of radiallyextending filament-like members.

5. The energy storage device of claim 4 wherein the members are disposedaround the full periphery of the hub means.

6. The energy storage device of claim 4 and further comprising matrixmeans disposed between the sheets and the members to bond said sheetsand members into a unitary structure.

7. An energy storage device having an axis of rotation extendingtransversely therethrough, comprising;

a plurality of anisotropic, filament-like members having maximumstrength-to-density along their longitudinal axes, the longitudinal axesof portions of said members extending radially from the axis of rotationof the device;

hub means having an axial channel extending therethrough, thelongitudinal axis of said channel being coincident with the axis ofrotation of the device, the hub means further having aligned bearings inthe walls of the axial channel,

.0 a shaft extending through the axial channel, the longitudinal axis ofthe shaft being. disposed coincident with the axis-of rotation of thedevice, the

shaft having a transverse opening formed therein and further havingaligned bearings formed in the walls of said transverse opening, and

a cruciform member disposed within the transverse opening and havingpairs of gimbal pins, one pair of said pins being rotatably receivedwithin the bearings in the shaft and the other pair of said pins, theaxes of which are disposed at right angles to the axes of thefirst-mentioned pair of pins, being rotatably received within thealigned hearings in the hub means, thereby allowing said hub means totilt relative to the shaft. g

8. An energy storage device having an axis of rotation extendingtransversely therethrough, comprising,

a plurality of anisotropic, filament-like members having maximumstrength-to-density along their longitudinal axes, the longitudinal axesof portions of said members extending radially from the axes of rotationof the device, and

hub means comprising arcuate side walls, the side walls being curvedtoward each other and toward the axis of rotation of the device.

9. The energy storage device of claim 8 wherein the filament-likemembers are held by the hub means in fixed, predetermined positions,portions of the members within said hub means being arcuate.

10. The energy storage device of claim 9 wherein the portions of themembers extending externally of the hub means are straight and alignedalong radii emanating from the axis of rotation of the device.

11. The energy storage device of claim 9, wherein the radius ofcurvature of the fixed arcuate portion of each of the members isdependent upon the distance of said member from a plane taken throughthe longitudinal axis of the device and perpendicular tothe transverseaxis thereof, theradius of curvature of each said member beingdetermined according to the relationship:

where:

R radius of curvature of a given member,

r== radius of the hub means; and.

D distance from the given member to the said plane. g

12. The energy storage device of claim 9 and further comprising matrixmeans for maintaining the members in fixed positions within the hubmeans.

13. An energy storage device having an axis of rotation extendingtransversely therethrough, comprising,

a plurality of anisotropic, filament-like members having maximumstrength-to-density along their longitudinal axes, the longitudinal axesof portions of said members extending radially from the'axis of rotationof the device, and

hub means for holding portions of the filament-like members, i

the members disposed in a plane through the longitudinal axis of thedevice and perpendicular to the transverse axis thereof being straightand the members on either side of said plane having portions within thehub fixed in predetermined arcuate configurations.

14. The energy storage device of claim 13 and further comprising matrixmeans for maintaining the members in fixed positions within the hubmeans.

15. The energy storage device of claim 13 wherein the portions of themembers extending externally of the hub means are. straight and arealigned along radii of the hub means.

16. The energy storage device of claim 13, wherein the radius ofcurvature of the fixed arcuate portion of each of themembers isdependenton the distance of said member from the said plane, the radiusof curvature of each said member being determined according to therelationship:

where:

R radius of curvature of a given member; r= radius of the hub means; andD distance from the given member to the plane. 17. In an energy storagesystem, a rotatable shaft, and

an energy storage structure having its midpoint mounted for tiltingmovement on the shaft and having an axis of rotation coincident with theaxis of rotation of the shaft when the longitudinal axes of across-section taken through the structure is perpendicular to the shaft,said structure comprising a plurality of anisotropic, filament-likemembers having maximum strengthto-density along their longitudinal axes,the longitudinal axes of major portions of said members extendingradially from the axis of rotation of the 12 device.

18. The energy storage system of claim 17, and further comprising hubmeans having an axial channel extending 'therethrough, the hub meansfurther having aligned bearings in the walls of the axial channel, theshaft extending through theaxial channel and having a transverse openingformed therein and further having alined bearings formed in the walls ofsaid transverse openings, and

a cruciform member disposed within the transverse opening and havingpairs of gimbal pins, one pair of said pins being rotatably receivedwithin the bearings in the shaft and the other pair of said pins, theaxes of which are disposed at right angles to the axes of thefirst-mentioned pair of pins, being rotatably received within thealigned bearings in the hub means, thereby allowing said hub means totilt relative to the shaft.

19. The energy storage system of claim 17, and further comprising hubmeans for holding the members in planes perpendicular to the axis ofrotation of the device.

20. The energy storage system of claim 19 wherein the members aredisposed around the full periphery of the hub means.

21. The energy storage system of claim 20 wherein the hub means isformed with a plurality of radially directedholes extending from thesurface of said hub means inwardly toward the axis of rotation of thestructure, each hole receiving therein a portion of one of said members.

1. An energy storage device having an axis of rotation extendingtransversely therethrough, comprising a plurality of anisotropic,filament-like members having maximum strength-to-density along theirlongitudinal axes, the longitudinal axes of portions of said membersextending radially from the axis of rotation of the device, hub meansfor holding the members in planes perpendicular to the axis of rotationof the device, the axis of rotation of the device being coincident withthe longitudinal axis of said hub means, the hub means being comprisedof disc-like layers of material, adjacent layers having confrontingsemi-cylindrical depressions in the upper and lower faces thereof, theconfronting semicylindrical depressions cooperating to receive portionsof each of the members within the hub means and said layers clampingsaid portions of said members in said depressions.
 2. The energy storagedevice of claim 1 wherein the adjacent lAyers are joined alongrespective upper and lower faces.
 3. An energy storage device having anaxis of rotation extending transversely therethrough, comprising aplurality of anisotropic, filament-like members having maximumstrength-to-density along their longitudinal axes, hub means for holdingthe members in planes perpendicular to the axis of rotation of thedevice, the axis of rotation of the device being coincident with thelongitudinal axis of said hub means and the longitudinal axes of themembers being aligned along radii emanating from points along the axisof rotation, the members being disposed around the full periphery of thehub means, the hub means being comprised of disc-like layers ofmaterial, adjacent layers having confronting semi-cylindricaldepressions in the upper and lower faces thereof, the confrontingsemi-cylindrical depressions cooperating to receive portions of each ofthe members within the hub means and said layers clamping said portionsof said members in said depressions.
 4. An energy storage device havingan axis of rotation extending transversely therethrough, comprising aplurality of anisotropic, filament-like members having maximumstrength-to-density along their longitudinal axes, the longitudinal axesof portions of said members extending radially from the axis of rotationof the device, and hub means comprising layers of parallel planar spiralwound filaments disposed in alternation with respect to parallel layersof radially extending filament-like members.
 5. The energy storagedevice of claim 4 wherein the members are disposed around the fullperiphery of the hub means.
 6. The energy storage device of claim 4 andfurther comprising matrix means disposed between the sheets and themembers to bond said sheets and members into a unitary structure.
 7. Anenergy storage device having an axis of rotation extending transverselytherethrough, comprising; a plurality of anisotropic, filament-likemembers having maximum strength-to-density along their longitudinalaxes, the longitudinal axes of portions of said members extendingradially from the axis of rotation of the device; hub means having anaxial channel extending therethrough, the longitudinal axis of saidchannel being coincident with the axis of rotation of the device, thehub means further having aligned bearings in the walls of the axialchannel, a shaft extending through the axial channel, the longitudinalaxis of the shaft being disposed coincident with the axis of rotation ofthe device, the shaft having a transverse opening formed therein andfurther having aligned bearings formed in the walls of said transverseopening, and a cruciform member disposed within the transverse openingand having pairs of gimbal pins, one pair of said pins being rotatablyreceived within the bearings in the shaft and the other pair of saidpins, the axes of which are disposed at right angles to the axes of thefirst-mentioned pair of pins, being rotatably received within thealigned bearings in the hub means, thereby allowing said hub means totilt relative to the shaft.
 8. An energy storage device having an axisof rotation extending transversely therethrough, comprising, a pluralityof anisotropic, filament-like members having maximum strength-to-densityalong their longitudinal axes, the longitudinal axes of portions of saidmembers extending radially from the axes of rotation of the device, andhub means comprising arcuate side walls, the side walls being curvedtoward each other and toward the axis of rotation of the device.
 9. Theenergy storage device of claim 8 wherein the filament-like members areheld by the hub means in fixed, predetermined positions, portions of themembers within said hub means being arcuate.
 10. The energy storagedevice of claim 9 wherein the portions of the members extendingexternally of the hub means are straight and aligned along radiiemanating from the axis of rotation of the device.
 11. The energystorage device of claim 9, wherein the radius of curvature of the fixedarcuate portion of each of the members is dependent upon the distance ofsaid member from a plane taken through the longitudinal axis of thedevice and perpendicular to the transverse axis thereof, the radius ofcurvature of each said member being determined according to therelationship: where: R radius of curvature of a given member; r radiusof the hub means; and D distance from the given member to the saidplane.
 12. The energy storage device of claim 9 and further comprisingmatrix means for maintaining the members in fixed positions within thehub means.
 13. An energy storage device having an axis of rotationextending transversely therethrough, comprising, a plurality ofanisotropic, filament-like members having maximum strength-to-densityalong their longitudinal axes, the longitudinal axes of portions of saidmembers extending radially from the axis of rotation of the device, andhub means for holding portions of the filament-like members, the membersdisposed in a plane through the longitudinal axis of the device andperpendicular to the transverse axis thereof being straight and themembers on either side of said plane having portions within the hubfixed in predetermined arcuate configurations.
 14. The energy storagedevice of claim 13 and further comprising matrix means for maintainingthe members in fixed positions within the hub means.
 15. The energystorage device of claim 13 wherein the portions of the members extendingexternally of the hub means are straight and are aligned along radii ofthe hub means.
 16. The energy storage device of claim 13, wherein theradius of curvature of the fixed arcuate portion of each of the membersis dependent on the distance of said member from the said plane, theradius of curvature of each said member being determined according tothe relationship: where: R radius of curvature of a given member; rradius of the hub means; and D distance from the given member to theplane.
 17. In an energy storage system, a rotatable shaft, and an energystorage structure having its midpoint mounted for tilting movement onthe shaft and having an axis of rotation coincident with the axis ofrotation of the shaft when the longitudinal axes of a cross-sectiontaken through the structure is perpendicular to the shaft, saidstructure comprising a plurality of anisotropic, filament-like membershaving maximum strength-to-density along their longitudinal axes, thelongitudinal axes of major portions of said members extending radiallyfrom the axis of rotation of the device.
 18. The energy storage systemof claim 17, and further comprising hub means having an axial channelextending therethrough, the hub means further having aligned bearings inthe walls of the axial channel, the shaft extending through the axialchannel and having a transverse opening formed therein and furtherhaving alined bearings formed in the walls of said transverse openings,and a cruciform member disposed within the transverse opening and havingpairs of gimbal pins, one pair of said pins being rotatably receivedwithin the bearings in the shaft and the other pair of said pins, theaxes of which are disposed at right angles to the axes of thefirst-mentioned pair of pins, being rotatably received within thealigned bearings in the hub means, thereby allowing said hub means totilt relative to the shaft.
 19. The energy storage system of claim 17,and further comprising hub means for holding the members in planesperpendicular to the axis of rotation of the device.
 20. The energystorage system of claim 19 wherein the members are disposed around thefull periphery of the hub means.
 21. The energy storage system of claim20 wherein the hub means is formed with a plurality of radially dirEctedholes extending from the surface of said hub means inwardly toward theaxis of rotation of the structure, each hole receiving therein a portionof one of said members.